To learn the Lua programming language visit http://lua-users.org/wiki/TutorialDirectory

To create games, press Escape to switch to the Editors Mode.
For a list of available API functions, check the official documentation webpage.

To edit system files, use "edit file.lua". If you mess something up, run "factory_reset" to revert the changes you've made.

Note that you will have to run "factory_reset" whenever a new update comes, so it's better to create a folder in drive D named "Programs" and place your own programs there.